Current processing of tungsten ores and other tungsten bearing materials involves their conversion to sodium tungstate solution, purification, and conversion to ammonium tungstate via liquid ion exchange techniques. Evaporation of the ammonium tungstate solution to a fraction of its initial volume results in the formation of tungsten products such as ammonium metatungstate, tungsten oxide, and tungsten metal. Typically, about 85% of the tungsten contained in the ammonium tungstate solution is recovered as ammonium paratungstate. At present, the other 15% that remains in solution is recycled back to the beginning of the process, that is, the caustic digestion of the material. This is inefficient, time consuming and costly.
A method to either increase the recovery of tungsten from ammonium tungstate as ammonium paratungstate and/or to recover the remainder of the tungsten from the ammonium paratungstate liquors without recycling through the process would be highly desirable and an advancement in the art.